Math Problem Statement

Factor and simplify: 10 cos^2(x) + cos(x) - 11

Solution

The problem asks to factor and simplify the following trigonometric expression:

10cos2x+cosx1110 \cos^2{x} + \cos{x} - 11

This looks like a quadratic equation in terms of cosx\cos{x}. Let's solve it step by step.


Step 1: Substitute u=cosxu = \cos{x}

This makes the equation:

10u2+u11=010u^2 + u - 11 = 0

Step 2: Solve the quadratic equation

Use the quadratic formula:

u=b±b24ac2au = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

where a=10a = 10, b=1b = 1, and c=11c = -11. Substituting these values:

u=1±124(10)(11)2(10)u = \frac{-1 \pm \sqrt{1^2 - 4(10)(-11)}}{2(10)}

u=1±1+44020=1±44120=1±2120u = \frac{-1 \pm \sqrt{1 + 440}}{20} = \frac{-1 \pm \sqrt{441}}{20} = \frac{-1 \pm 21}{20}

This gives two solutions:

  1. u=1+2120=2020=1u = \frac{-1 + 21}{20} = \frac{20}{20} = 1
  2. u=12120=2220=1110u = \frac{-1 - 21}{20} = \frac{-22}{20} = -\frac{11}{10}

Step 3: Back-substitute u=cosxu = \cos{x}

  • For cosx=1\cos{x} = 1, the solution is:

    x = 0 + 2k\pi \quad \text{(where k is any integer)}

  • For cosx=1110\cos{x} = -\frac{11}{10}, this is impossible because cosx\cos{x} is bounded by 1cosx1-1 \leq \cos{x} \leq 1.


Step 4: Factor the original expression

Using the valid solution cosx=1\cos{x} = 1, the factorization of the quadratic equation corresponds to:

10(cosx1)(cosx+1110)=010(\cos{x} - 1)(\cos{x} + \frac{11}{10}) = 0

However, since cosx=1110\cos{x} = -\frac{11}{10} is not a valid solution, the only valid factorization relevant to real solutions is:

10(cosx1)=010(\cos{x} - 1) = 0


Final Answer:

The solution to the equation is:

cosx=1\boxed{\cos{x} = 1}

Thus, x=0+2kπx = 0 + 2k\pi, where kk is any integer.


Do you need further clarification or have any questions?


Here are 5 related questions for deeper understanding:

  1. How can we solve other trigonometric equations with quadratic forms?
  2. What are the bounds of cosx\cos{x} and sinx\sin{x}, and why do they matter?
  3. What is the difference between factoring and solving a trigonometric equation?
  4. How does the quadratic formula work in more complex trigonometric contexts?
  5. Can other substitution methods help with trigonometric equations?

Tip: Always check the domain constraints when dealing with trigonometric functions to avoid extraneous solutions!

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Trigonometry
Quadratic Equations
Factoring

Formulas

Quadratic equation formula: ax^2 + bx + c = 0
Cosine function: cos(x)

Theorems

Quadratic formula
Cosine properties

Suitable Grade Level

Grades 11-12